(1) Field of the Invention
This invention relates to a method for producing diarylmethane or its derivatives which are useful as high boiling point aromatic solvents and intermediate compounds for producing various kinds of chemical substances. More particularly, the invention relates to a method for producing diarylmethane or its derivatives from easily available compounds of simple structure such as alcohol, formaldehyde and aromatic compounds.
(2) Prior Art
As the methods for producing the diarylmethane, it is proposed to condense aromatic compounds with several condensing agents. For example, it is proposed that various condensing agents such as halogenated hydrocarbon, formaldehyde or its aqueous solution as formalin are condensed with aromatic compounds in the presence of a catalyst.
A method to use formaldehyde or its aqueous solution of formalin as a condensing agent is preferable because they are inexpensive. In this method, water is generated as a result of condensation. So that, it is not desirable because a by-product water sometimes impairs the activity of acid catalyst or it dilutes the catalyst. For example, in the methods disclosed in J. Frederic Waker, FORMALDEHYDE, 3rd Ed.; U.S. Pat. Nos. 3,043,886; and 2,981,765; and Japanese Laid-Open Patent Publication No. 2-134332, the condensation reaction of aromatic hydrocarbons is carried out using formaldehyde as a condensing agent and sulfuric acid or aluminum chloride as a catalyst. In examples in the above disclosure, when a catalyst such as sulfuric acid or aluminum chloride is used, the subsequent treatment for used catalyst is difficult, in addition, even when adequate reaction conditions are employed, highly condensed products having three or more benzene rings are undesirably produced in addition to an intended product.
The reaction of condensation using a condensing agent of formaldehyde and a solid acid catalyst of zeolite is disclosed in Applied Catalysis, 51, 113-115 (1989); U.S. Pat. Nos. 4,011,278; 4,306,106; 4,476,330; and 4,895,988; and Japanese Laid-Open Patent Publication No. 1-180835. In the reaction disclosed in these references, although the dilution of catalyst owing to by-product water is not caused because solid acid catalysts are used, the lowering of catalytic activity cannot be avoided. Furthermore, the condensation using a condensing agent of formalin as an aqueous solution of formaldehyde in the presence of zeolite catalyst is disclosed in the foregoing U.S. Pat. No. 4,895,988 and Japanese Laid-Open Patent Publication No. 1-180835. In these cases, the catalytic activity is not satisfactory because the condensation is done in the presence of water from the beginning stage. Accordingly, in these examples, the condensation of reactive phenol is mainly done.
Furthermore, several methods of condensation using halogenated hydrocarbons as condensing agents are well known in the prior art. Some of them are put into industrial practice. The by-products of halogenated hydrocarbons have not especially undesirable influence on the condensation reaction. However, the method involves several problems caused by the by-product hydrogen halide, such as the troubles in after-treatment, remained chlorine in the obtained product, and corrosion of apparatus. Furthermore, the problem concerning the polyhalogenated aromatic compounds produced by side reactions is posed recently.
In view of the above-described state of prior art to produce the diarylmethane which is useful as high-boiling aromatic solvents and as intermediates for various kinds of chemical products, it is eagerly wanted to propose an industrially workable method for synthesizing diarylmethane without difficulty and on a high yield using a novel condensing agent.
By the way, it is to be noted that the term "condensing agent" herein referred to means one of reactants used in the condensation reaction and it is bifunctional in the condensation. With its bifunctional property, it can couple two molecules of aromatic hydrocarbon of the other reactant in the condensation. The number of functional groups in an aromatic hydrocarbon in the condensation reaction basically corresponds to the number of hydrogen atoms connected to the benzene ring. However, all the hydrogen atoms on the benzene ring have not always the same reaction characteristics because of the orientation.